1. Field of the Invention
The present invention relates to a linear motion rolling guide unit which is applied to sliding portions of machining tools and various processing equipment and which consists of a track rail with raceway grooves formed longitudinally extending on both side walls thereof, a casing saddling the track rail and having raceway grooves, and a number of rolling elements that roll between the facing raceway grooves.
2. Description of the Prior Art
In a conventional linear motion rolling guide unit, a slider that slides on a track rail consists of a casing, end caps fixed to both ends of the casing, end seals attached to the end caps, and an under seal provided to the underside of the slider. The linear motion rolling guide unit further consists of: a number of rolling elements that travel rolling in a raceway formed between the raceway groove on the track rail and the raceway surface on the casing; and a retainer fixed to the casing to hold the rolling elements in the casing.
As an example of such a linear motion rolling guide unit, there is a four-raceway endless linear motion rolling guide unit. The four-raceway endless linear motion rolling guide unit will be explained by referring to FIGS. 2, 3 and 4. FIG. 2 is an example perspective view of the four-raceway linear motion rolling guide unit. FIG. 3 is an end view of the four-raceway endless linear motion rolling guide unit of FIG. 2. FIG. 4 is a cross section taken along the line A--A of FIG. 2.
The four-raceway endless linear motion rolling guide unit has a track rail 1 with almost and I-shaped cross section, a slider 2 saddling the track rail 1 in such a way that it can move relative to or slide on the track rail 1, and a number of cylindrical rolls 3 rotatably interposed between the track rail 1 and the slider 2. The track rail 1 is formed with recessed grooves 8 longitudinally extending on both sides 18 thereof, which form raceway surfaces 5, 6. The recessed grooves 8 of the track rail 1 are formed at the upper and lower edges with a longitudinally extending upper raceway surface 5 and lower raceway surface 6 formed on slant surfaces. The slider 2 has a casing 4 which is formed with the recessed portion 10 so that the casing can saddle the track rail 1, and end caps 7 attached to both longitudinal ends of the casing 4. To seal the boundary between the track rail 1 and the slider 2 when the slider 2 slides on the track rail 1, the ends of the end caps 7 are each provided with an end seal 20 and the underside of the slider 2 with an under seal 22.
The recessed portion 10 of the casing 4 is formed with a longitudinally extending upper raceway surface 11 and lower raceway surface 12 at locations facing the upper raceway surface 5 and the lower raceway surface 6 of the track rail 1. Between the upper raceway surface 11 and the lower raceway surface 12 of the casing 4 is formed a longitudinally extending engagement V-shaped groove 15, which engages with an engagement projection 16 formed on the retainer 9 which extends longitudinally. A part of the retainer 9 is loosely fitted in the recessed groove 8 of the track rail 1 and screwed and fixed by bolts 17 inserted through the bolt insertion hole 26 formed in the casing 4.
In the above construction of the 4-raceway endless linear motion rolling guide unit, two raceways are formed on each side of the track rail 1, one by the upper raceway surface 5 on the track rail 1 and the upper raceway surface 11 on the casing 4 and the other by the lower raceway surface 6 on the track rail 1 and the lower raceway surface 12 on the casing 4. Hence, a total of four raceways are formed on both sides of the track rail 1. In these loaded roller raceways, a number of cylindrical rollers 3 roll in contact with the facing raceway surfaces 5 and 11, 6 and 12. The casing 4 is formed with return passages 13, 14, and the end caps 7 are formed with direction changing passages (not shown), that connect the loaded roller raceways and the return passages 13, 14. Hence, two endless circulating passages are formed by the loaded roller raceways, the direction changing passages and the return passages 13, 14.
The endless circulating passages may, for example, have different lengths and be disposed one inside the other. That is, a smaller endless circulating passage may be arranged inside the loop of a larger endless circulating passage and disposed at right angles with each other so that they will not interfere with each other. The larger and smaller endless passages have the same length of the loaded roller raceways. As the slider 2 moves along the track rail 1,, the cylindrical rollers 3 circulate through the large and small endless circulating passages. It is also possible to make the endless circulating passages cross each other so that they can be formed in the same length.
Such a four-raceway endless linear motion rolling guide unit is cited, for example, in the Japanese Patent Laid-Open No. 175564/1989, Japanese Utility Model Laid-Open No. 63812/1992, and Japanese Patent Application No. 166326/1991.
In the conventional four-raceway endless linear motion rolling guide unit, the process of mounting the end caps 7 on the casing 4 consists of: positioning the end caps on the casing 4 precisely; forming two endless circulating passages by the loaded roller passages, the direction changing passages and the return passages 13, 14 to allow for smooth circulation of rollers 3; and forming an appropriate sliding surface at the boundary between the track rail 1 and the slider 2.
In the conventional four-raceway endless linear motion rolling guide unit, the end caps 7 are mounted to the casing 4 generally by forming positioning holes in the casing 4 and then positioning the end caps 7 with respect to the casing 4. However, since the heat-treatment of the casing 4 and the end cap 7 causes their deformation and since the casing 4 and end caps 7 are subject to the machining process, the precise positioning of the end caps 7 with respect to the casing 4 cannot be made even if the casing 4 is formed with the positioning holes.